1. Technical Field of the Invention
The present invention relates in general to optical systems, and in particular to optical systems including aspherical optical elements.
2. Description of Related Art
Aspherical or acylindrical optical elements have optical surfaces with profiles that do not form a portion of sphere or cylinder, respectively. The most common fabrication methods for aspherical or acylindrical optical elements include molding (for small size aspherical surfaces) and grinding and polishing (for larger surfaces). Aspherical or acylindrical optical elements are typically used for reducing optical aberration, optical system size, weight and manufacturing cost in various applications, such as optical scanning and beam shaping.
In optical scanner systems, the three basic scanning configurations are: objective scanning, post-objective scanning and pre-objective scanning. In objective scanning, the objective or the light source or both are moved. The movement can be, for example, a rotation about a remote axis or a translational motion. The moving objective can include a reflective mirror, a refractive lens, or a diffractive element. In such systems, the objectives are typically displaced a short distance relative to their focal length to avoid output beam distortion and varying spot size from one scanning angle to another. Thus, the resulting beam scanning angle is typically limited to 30-40°, which is considered to be a wide angle for a microsystem scanner Angles larger than 40° typically produce severe spot size distortion.
In pre-objective and post-objective scanning, the optical beam is rotated by reflection from a flat rotating mirror (or polygon) either before or after the objective lens, respectively. Aspherical surfaces are typically utilized in the pre-objective scanning configuration to form an “f-theta lens,” which produces uniform or close to uniform beam size in order to focus the scanned beam on a flat plane instead of a curved plane.
What is needed is a type of optical surface that can produce larger scanning angles and be utilized in any type of scanning configuration.